Along with the computerization of offices in the 1980's came electronically controlled non-impact printers such as the ink jet and laser printers. Drop-on-demand inkjet printers can be piezo or thermal (bubble jet). In piezo ink jet systems, ink drop-lets are ejected by an oscillating piezo crystal. However, the thermal ink jet dominates the drop-on-demand photo ink jet market. In this system, rapid heating behind the ink nozzles cause a bubble of vapor to form in the ink. The resulting bubble expansion and ink ejection from the inkjet printer cartridge causes printing to appear on the substrate.
Full-color inkjet printers are more common than color lasers and are much more economical. The main advantage of inkjet printers over lasers and other non-impact printing techniques include their low cost and simplicity. Thermal inkjet systems are capable of dispensing ink rapidly and accurately. The technology of this and other inkjet systems are discussed in the Chemistry and Technology of Printing and Imaging Systems, edited by P. Gregory, published by Chapman & Hall, 1996. Representative thermal inkjet systems and cartridges are discussed in U.S. Pat. No. 4,500,895 to Buck et al., U.S. Pat. No. 4,513,298 to Scheu, and U.S. Pat. No. 4,794,409 to Cowger et al., which are all hereby incorporated by reference.
The technology of inkjet printers has undergone many changes and improvements since they first appeared. Research has been conducted to ensure that the images produced are of consistent high quality. Thus, it is important that the images be permanent by being lightfast, airfast, and stain resistant, and the like when exposed to the atmosphere, light, and daily use by typical consumers. Another important feature is print quality. The image must appear uniform in gloss, especially for photographic printing.
As used herein, air fastness will mean that the images do not fade when exposed to the atmosphere. Air fastness is a measure of permanence as used herein. Air fastness is measured by exposing printed images to gas in a chamber and comparing print density before and after the exposure.
Another desired feature of printed images is light fastness. As used herein, light fastness will mean that the images do not fade when exposed to light. Light fastness is another measure of permanence as used herein. Light fastness is measured by exposing printed images to intense light in light chambers (fadomers) and comparing print density before and after the exposure.
Dye based inkjet ink produces super image quality, or photo quality, with gloss media type substrates. However, the images can not last very long due to light and gas fade. Currently, there are two commonly used ways of addressing this problem: 1) laminate the printer image with a coating; or 2) use pigmented ink instead of dye based inks. The first approach is costly and adds complexity to the printing process. The second approach faces the challenge of matching the photo and image quality of the dye based ink. To help solve the problem associated with pigmented inks, many in the industry use porous semi-gloss media that allows fast dry and good spreading of the pigmented ink. As a result, the inked area has high gloss from the pigment ink formula and good image quality, but the areas without print, or white areas, have loss gloss. This produces an objectionable non-uniform glossy surface when viewed.
As stated above pigmented inks for photographic printing requires, among other things, fast-drying glossy media. By “photographic printing” is typically meant graphic art and photographic prints, typically from digital. Examples of such printers include Hewlett-Packard's DesignJet series (2000, 2500CP, 2800, 3500CP, 3800, 5000, 5000PS); an example of a glossy media printer includes Hewlett-Packard's Photosmart Printer. The afore-mentioned printers print on porous, glossy media, among others.
Thus, an ink composition is required that eliminates, or at least minimizes, the foregoing problems, while providing improved image quality print on porous, or hybrid porous glossy or semi-glossy media, consistent with silver halide photography.
Moreover, this invention provides durability and stain resistance to photos printed with pigmented inks such that lamination is not needed.